A known fuel system of this type has four hydrogen tanks connected in parallel to a filling port by filling piping and to a fuel cell by supply piping (see Patent Document 1). The filling piping which connects the filling port to the hydrogen tanks comprises a single inlet pipe and four branch outlet pipes. The supply piping which connects the hydrogen tanks to the fuel cell comprises four inlet pipes and a single merged outlet pipe.
Inspecting for hydrogen leakage from the branching or merging part of the pipes, from the pipes themselves or the like, that is, leak checking, is essential for the fuel cell system. The system described in Patent Document 1 introduces an inert gas through the filling port to perform leak checking of the filling piping. The system also introduces an inert gas through a leak checking point (valve) provided on the supply piping to perform leak checking of the supply piping.